1. Field of the Invention
The present invention relates to a micromotion mechanism having an ultrasonic motor, and more specifically to a micromotion mechanism for positioning a moving element supported such that the element can be moved with respect to a fixing base.
2. Description of the Related Art
A microscope is widely used in observing the microstructure of a semiconductor, a living body sample, etc. An XY stage is used in setting an optional position of an observation target for a microscopic observation. In this case, a feed resolution and the stability in a static position demanded for a microstructure to be observed are required. In addition, it is often necessary to observe plural positions of an observation object with high throughput, thus high-speed operation is also required.
One of the actuators corresponding to the above-mentioned requests is an ultrasonic motor. For example, as described in the patent document 1 (Japanese Published Patent Application No. 2005-265996), there is an apparatus proposed using an ultrasonic motor as an actuator of the XY stage for a microscope. There is also the configurations described in the patent document 2 (Japanese Published Patent Application No. H7-264880) and the patent document 3 (Japanese Patent Publication No. 3184117) as an ultrasonic motor and its holding method.
Recently, with more miniaturization of observing submicroscopic objects such as observing a stroke width of a semiconductor, observing a molecule of a living body, etc., the magnifying power of a microscope is also getting higher. Thus, high drive resolution of an ultrasonic motor for the microscope in a submicron order has been required. Furthermore, for example, an apparatus such as an incubator for living body sample can be mounted on a stage of a microscope. In this case, a bending resistance such as a carrying load, wiring, etc., and external force such as a touch of a hand etc. require large static holding and drive force of an ultrasonic motor.
On the other hand, the ultrasonic motor moves a moving element by the friction when it presses the oscillator onto a moving element. In the case of microscopic drive in a submicron order, the pressing force on the oscillator onto the moving element changes the amount of movement of the moving element. For example, microscopic drive is made on a certain drive condition in a drive mechanism having the configuration as shown in the schematic chart of FIG. 1, there is the relationship shown in FIG. 2 between the pressing force and the amount of movement.
The drive mechanism shown in FIG. 1 includes a fixing base 31, a moving element 33 supported by a guide 32 such as a linear ball guide etc., which is movable with respect to the fixing base 31, an oscillation element 35 provided with a projection unit 34 (34a and 34b) contacting the moving element 33, a holding member 36 for holding the oscillation element 35 with respect to the fixing base 31. In this case, for example, if the oscillation element 35 is microscopically driven by the application of a drive signal with the oscillation element 35 pressed against the moving element 33 through the projection unit 34 with the pressing force F, then the moving element 33 is moved along the guide 32 by the amount of movement S. In FIG. 2, the vertical axis indicates the amount of movement S and the horizontal axis indicates the pressing force F.
As shown in FIG. 2, the amount of movement S increases with the increase of the pressing force F, and the amount of movement S is the maximum with the pressing force FOP. Afterwards, the amount of movement S decreases, and the moving element 33 does not move any more or moves backwards after the pressing force Fmax is exceeded. Thus, it is necessary to load the optimum pressing force FOP to correctly and efficiently obtain the microscopic drive.